docs: def split_coords_3d(seq):
      """
      :param seq: a flat list with lons, lats and depths
      :returns: a validated list of (lon, lat, depths) triplets
  
      >>> split_coords_3d([1.1, 2.1, 0.1, 2.3, 2.4, 0.1])
      [(1.1, 2.1, 0.1), (2.3, 2.4, 0.1)]
      """
      lons, lats, depths = [], [], []
      for i, el in enumerate(seq):
          if i % 3 == 0:
              lons.append(valid.longitude(el))
          elif i % 3 == 1:
              lats.append(valid.latitude(el))
          elif i % 3 == 2:
              depths.append(valid.depth(el))
      return list(zip(lons, lats, depths))